Myocardial ischemia causes a drop in state 3 QO2 which we now feel is due to an impairment of electron flow through complex 1 of the electron transport chain. At 14 microM free calcium, lowering of pH from 6.8 to 6.0 causes a slower rate of E approximately P formation and decomposition for cardiac sarcoplasmic reticulum which might account for some of the loss of SR function seen during the acidosis that occurs during ischemia. Changes in pH also affect calcium binding to the calcium specific sites of troponin and probably accounts for the pH shifts seen in the calcium dependence of tension development and actomyosin ATPase. Methods for isolating functional cardiac myofibrils which retain the level of P-light chain phosphorylation and TN-1 phosphorylation which existed in beating hearts at the time of freeze clamping have been developed and applied to control rabbit hearts beating in situ. Cardiac SR is phosphorylated by c-AMP dependent protein kinase. The substrate for this phosphorylation is a 22,000 dalton protein. Vanadium alters the contractility of cardiac muscle. It inhibits Na, K ions- ATPase activity and stimulates adenyl cyclase. It alters the affinity of a potassium site and a phosphate site, both of which regulate (3H)ouabain binding to Na, K ions-ATPase. Tryptic peptides of the catalytic subunit of Na, K ions-ATPase have been isolated. Lipoprotein lipase has been purified from bovine milk. The mechanism of action is under investigation. Using monomolecular films of lipid, apoC-11 prevents surface denaturation of the enzyme and also specifically activates the lipase. A specific, highly sensitive method has been developed to monitor lipolysis.